The present invention is concerned with a test device for the determination of the strength of adhesion of a protective lacquering on the body of a collapsable tube, which device comprises a base plate with a recessed seating for the shoulder of a tube with threaded neck and a compressing mechanism engaging the upper open end of the tube body, the compressing mechanism being movable against the base plate.
Cylindrical and conical tubes made of aluminium are provided internally and externally with a protective lacquering which must have a high adhesive strength in order that it does not tear or loosen from the aluminium in the case of deformation by squeezing or rolling up in the course of emptying the tube since, in the case of the internal protective lacquering, this would result in an impairment of the contents of the tube.
For testing the protective lacquering, hitherto a test device has been used which has a guide column. The inventive test device includes a passage of a guide mandrel which is loosely placed in the interior of the tube. The tube casing is manually pressed together concertina-like by pressure which is as uniform as possible with a predetermined rate of compression of 100 to 400 mm/s of the tube body. The compressed tube body is then removed from the test device and manually pulled out in the axial direction. The compression edges of the pulled-out tube are investigated visually for crack formation or for loosening of the internal and external protective lacquering. In the case of this manually operated compression device, the maintenance of the predetermined rate of compression is difficult and, in the case of a series of tubes to be tested, can practically not be reproduced. Furthermore, the manual pulling out of the compressed tubes is laborious and requires a great amount of strength. Since twisting and bending of the tube body can thereby not be excluded, such accidental additional stresses can falsify the results of the test.